Stephane Ascoet via rsync <> wrote:
> Kevin Korb <> le 29/06/2023 22:43:
> > Are you so sure rsync actually copies the file? It should
> > correct the timestamp and tell you it did.
> Of that what it should do! But I'm sure not: the target is a very 
> low-quality-and-performance USB key ... less than 3 kb/s. And
> looking the FS during the transfer, I saw the temporary files
> being written. And since I was using --backup, the files has been
> backuped...  only to be replaced by exactly the same thing :-(
> So this disable a lot of interest in Rsync :-( Isn't there a way
> to disable "--whole-file"?

Short answer:  Last I heard, no, for (what rsync sees as) "local"
transfers.  And I agree that there should be, at least when the
target is a flash device -- but it might not help much with your

Longer answer, with details:  rsync believes that, for any transfer
which it sees as local (and this includes NFS, CIFS, etc. which are
mapped into the local namespace although the data may in fact be
accessed over a network), overwriting the destination -- even with
what may be the same data -- is at least as fast as reading it first
to determine whether it needs to be overwritten.  This belief was
usually accurate before the advent of read-mostly technologies (like

However, when the target is on a flash device, --whole-file creates
a couple of problems:

* Most flash devices, including but not limited to USB "thumb drives,"
  can be read substantially faster than they can be written.

* Even if there were no speed difference, overwriting -- even with
  the same data -- typically imposes wear on the flash device.
  (There may be a few which internally do a read-before-write, and
  avoid overwriting the same data.)

As to your situation, I suspect you may be dealing more with transfer
speed (via a USB 1.1 port?) than with read/write speed differences.
The rsync assumption that reading is no faster than writing may well
be accurate with this "low-quality-and-performance USB key."

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